How useful are direct alpha-measurements of fecal ash? What are their limits?

Abstract

The Cogema Radiotoxicology Laboratory at La Hague carries out more than 40 000 analyses per year. This figure includes approximately 12 000 systematic detections of actinides in urine and more than 400 analyses of actinides in feces performed following suspicion of an internal contamination incident. The radiochemical analysis of feces, which involves fractionated separation, is a difficult and time-consuming technique which is poorly suited to emergency detections of artificial radioelements. With feces that may contain artificial activity, the laboratory, therefore, uses a feces screening method consisting in a global α count of the fecal ash. This method requires the preliminary determination of the background of the natural environmental radioactivity. This prompted our laboratory to carry out a global α-count of the fecal ash of 30 people that both work on the site and live in the region but who are not exposed to artificial α radioelements. A threshold value of 0.2 Bq/g of natural uranium and its derivatives in fecal ash was established.